When a drill hole is created in the ground, in particular a horizontal drill hole in the ground, a cavity is usually created that extends at an angle, in particular close to 90°, from the earth's surface into the ground. The drilling device, in particular a horizontal drilling device, is lowered into the cavity, which can also be described as a construction trench or an access trench. From the cavity, it is then possible to create a horizontal drill hole, in particular, using the drilling device.
In areas in which buildings have been erected, the cavity in which the drilling device is to be positioned must have a relatively small diameter. Such a small cavity is known as “keyhole technology” in the context of trenchless installation and replacement of gas, water, power or data lines for building connections. Surface work should be reduced to a minimum, in particular in areas in which buildings have been erected, in which the ground is covered with a top surface. Keyhole technology results in less of the consequential surface damage and consequential surface costs known from the open construction method. The earthwork and surface work can be realized more safely, on a smaller scale and more productively. The creation of a horizontal drill hole in the ground using keyhole technology is described in DE 10 2010 013 725 A1, for example.
In order to create a round cavity in ground covered with a top surface, a core bit in the form of a core drill is usually used initially. The top surface is cut in a circular shape by means of the core drill, with the external diameter of the core drill corresponding to the external diameter of the cavity to be created. Once the circular cut has been made, the core drill is removed and, using a core drill or another drill of lesser diameter, an additional drill hole is created, by means of which the drill core can be removed from the cavity. Three work steps are thus usually required in order to create a cavity:                1. Making a circular cut in the surface corresponding to the external diameter of the cavity to be created and removal of the core drill,        2. Creating an additional drill hole inside the circular cut made previously and        3. Removal of the drill core through lifting out of the drill core by means of a rod system introduced into the additional drill hole.        
Based on this prior art, the objective of the invention is to create an improved top surface drilling device and a method for drilling a core in a top surface, by means of which a cavity can be created more efficiently, and, in particular, the number of method steps can be reduced.